This invention relates generally to cooling systems that employ cooling evaporators and in particular the invention relates to method and apparatus for defrosting such evaporators.
Typical cooling systems for refrigeration appliances such as refrigerators and freezers for example include an evaporator, oftentimes in the form of a coil, on which frost and ice can be formed and accumulate over a period of time. The accumulation of frost and ice on the evaporator results in the inefficient and more costly operation of the cooling system. Consequently, it is necessary to remove the frost and ice accumulation so that the cooling system can operate in an effective manner.
A practice often employed for defrosting and removing frost and ice that has accumulated or built up on an evaporator coil is to provide a heater, usually of high wattage, to heat the evaporator coil and melt the accumulated ice. Typically, a resistive heater is used and the heater tends to dissipate heat in all directions so that not only is the evaporator coil heated but the surroundings of the evaporator coil are heated as well. As a result, the compartment where the evaporator is located such as the freezer compartment or fresh food compartment of a refrigerator for example can be heated to a degree.
The frequency at which defrost cycles are carried out can be based on the passage of time using a mechanical timing device that both initiates and terminates the defrost cycle. Alternatively, an electronic circuit can be provided to control the defrost cycle using a thermostat or the like to measure the temperature at the evaporator and employing defrost algorithms.